Chair back



FIG. 1 is a right rear perspective view of a chair back showing my new design, the left side being a mirror image thereof;

FIG. 2 is a front elevational view thereof; and,

FIG. 3 is a cross sectional view taken along line 3--3 of FIG. 2.

The broken lines shown in FIG. 1 are for environmental purposes only and form no part of the claimed design. 

The ornamental design for a chair back, as shown and described. 